| Year | Value (SE) |
|---|---|
| 2009 | 0.7900 (0.0125) |
| 2010 | 0.8570 (0.0493) |
| 2011 | 0.7850 (0.0079) |
| 2012 | 0.7580 (0.0102) |
| 2013 | 0.8350 (0.0255) |
| 2014 | 0.6860 (0.0184) |
| 2015 | 0.7440 (0.0192) |
| 2016 | 0.9040 (0.0104) |
| 2017 | 0.7900 (0.0165) |
| 2018 | 0.7490 (0.0243) |
| 2019 | 0.6790 (0.0174) |
| 2020 | 0.9410 (0.0352) |
| 2022 | 1.0160 (0.0300) |
| 2023 | 0.9340 (0.0182) |
